πταίω
I. trans. "to make to stumble or fall", τινὰ πρός τινι Pind.:—Pass., τὰ πταισθέντα "failures", Luc.
II. intr. "to stumble, trip, fall", Soph., etc.; πτ. πρός τινι "to stumble against, fall over", Aesch., Plat.; πρός τι Xen.; also, μὴ περὶ Μαρδονίωι πταίσηι ἡ Ἑλλάς lest Hellas "should get a fall" over him, i.e. be defeated by him, Hdt.
2. metaph. "to make a false step, to fail", Thuc., Dem.; so, ἐλάχιστα, τὰ πλείω πτ. Thuc. etc.